Refusal of moving reservation dates - Unclear policies

Good day

Beekman is refusing to amend dates for my booking. They are saying amending dates is actually cancelling. Which is odd because this is not clearly outlined in their booking confirmation policy. The policy only talks to cancelation. Apparently it is not allowed to change dates if you are required to occupy the room within 21 days. I believe that such information should be documented and communicated upfront other than when one is asking to change. Life happens and people have other commitments, so if amendments cannot be allowed it is fair if Beekman is upfront about the terms of amendments. Amendments is not in any way a cancelation. I called the centre and even the Manager refused to hear my concerns. I am not happy at all that they are not taking accountability for the loophole in their own policy but rather making a customer suffer.